The LCD (Liquid Crystal Display has been widely accepted by people due to its characteristics of lightness, thinness, low power cost and so on. Although the LCD has greatly reduced screen flicker than the CRT (Cathode Ray Tube) display, it still has some flicker. The screen flicker easily causes a person's visual fatigue and also reduces the use life of the LCD.
The reason for LCD flicker is the nonuniform brightness of pixels on the display panel. The pixel brightness depends on the deflection of the liquid crystal molecule and is proportional to the driving voltage of the pixel, and the driving voltage usually takes a common voltage Vcom as a reference. Due to the variance of manufacturing process, the common voltage reference points for different pixels of the same LCD panel would be different, but the common voltage supplied for different pixels are practically the same, which results in brightness nonuniformity of pixels and thus the screen flicker phenomenon. For example, the common voltage for a LCD panel is generally set as 5.5 V at the manufacturer, while the driving voltage levels for pixels are between 0V and 10V. As such, within the entire voltage range, different areas of the same LCD panel would have different sectional voltage values. The driving voltage for some areas is practically 4.5 V while that for other areas can be 5.5 V. As for the entire voltage range, different sectional voltages would cause different pixel brightness, thereby resulting in the screen flicker phenomenon. In other words, the flicker of the LCD panel comes from the nonuniform brightness of pixels due to the offset of the common voltage Vcom.
Generally, many LCD panel manufacturers adjust the common voltage before releasing the products, but such adjustment is a one-time adjustment before releasing. The voltage Vcom may offset due to time and temperature among others during practical usage; therefore, such a one-time adjustment cannot reduce screen flicker essentially. In addition, the adjustment of the common voltage Vcom before releasing is usually performed manually by additionally adding an adjustment resistor. Such an adjustment has low precision and low efficiency.